1. Technical Field
The present invention relates to an image forming apparatus which charges an electrostatic latent image carrier by applying a charging bias having an alternating-current component to a charging member opposed to the electrostatic latent image carrier while defining a specified gap, and an abnormality determination method for such an image forming apparatus.
2. Related Art
For an image forming apparatus for forming an image by forming an electrostatic latent image on the outer surface of an electrostatic latent image carrier charged to a specified surface potential and developing the electrostatic latent image, technology for detecting a charging failure of the electrostatic latent image carrier has been proposed to prevent an image defect and the damage of the apparatus resulting from the charging failure of the electrostatic latent image carrier. For example, in an image forming apparatus disclosed in JP-A-2004-85902 (FIG. 5 for instance), a photosensitive member as the electrostatic latent image carrier is charged by applying an alternating-current bias to a charging roller held in contact with the outer surface of the photosensitive member and the presence or absence of a charging failure is determined by detecting the distortion of a charging current through the comparison of an average value and a peak value of the charging current flowing into the charging roller.
The above technology is applicable to apparatuses adopting a contact AC charging method, in which a charging member having an alternating-current bias applied thereto is held in contact with an electrostatic latent image carrier. As a different charging method, there is a non-contact AC charging method for applying an alternating-current bias to a charging member arranged at a specified gap from the electrostatic latent image carrier. However, not many proposals have been made for the technology for detecting a charging failure in the non-contact AC charging method. Particularly, as a problem peculiar to the non-contact AC charging method, abnormal discharge occurs in the gap between the electrostatic latent image carrier and the charging member and such abnormal discharge leads to a charging failure and the damage of the apparatus. However, the technology for detecting the charging failure resulting from such abnormal discharge has not been sufficiently studied thus far.
Further, in an image forming apparatus including a plurality of image forming stations, a bias power supply is shared by the plurality of image forming stations to reduce the number of parts and to downsize the apparatus. In such a case, it has been difficult to specify the image forming station having an abnormality even if an abnormal discharge should be detected based on the waveform of the current.